13C Spin-lattice relaxation times of piperidines. Molecular motions and interactions with solvents
Abstract
13 C Spin-lattice relaxation times have been measured for piperidine (1) and N-methylpiperidine (2) in several different solvents [CDCl3, CD3OD, D2O, (CD3)2CO, C6D12, C6D5NO2, and (CD3)2SO], and have been analysed in terms of anisotropic molecular motion. The results of these calculations show that these solvents can be divided into three types according to the hydrogen-bonded solute–solvent interaction involved: (i), C6D12, C6D5NO2, and (CD3)2SO, which have no effect on molecular rotation; (ii), CDCl3, CD3OD, and D2O, in which hydrogen-bonded interactions between solute and solvent molecules caused by the nitrogen lone-pair are expected (these affect the apparent size and anisotropy of the solute molecule, depending on the orientation of the lone-pair); and (iii), (CD3)2CO, in which the carbonyl group interacts with the solute NH proton.